Many inkjet printers contain cyan, magenta and yellow pens that share the same printhead. Because of this printhead sharing, exit orifice diameters for all three pens are very similar and the resulting pen drop volumes are nearly identical. Therefore, even when pens are changed, colors tend to remain in balance for any given image that is printed out. However, there are a few exceptions to this type of inkjet printer, and these exception printers use independent color pens that do not necessarily correlate well with each other. These exception pen sets can cause noticeable hue shifts in color images unless the pen manufacturing process exhibits extremely tight tolerances. Such color shifts could make blue skies have a greenish tint or a red apple appear orange. Due to the dramatic negative effect this can have on print quality, many such printers allow the user to compensate with a manual color calibration process.
Earlier versions of Manual Color Calibration (MCC) for inkjet printers incorporated aspects of a color to black ink relationship. The MCC developed for one earlier version of a printer is shown in FIG. 1A and comprises a 3×3 pattern of test bars. The MCC developed for another earlier version of a printer is shown in FIG. 1B and expands the original pattern to a 7×7 pattern of test bars. The pattern used in both prior art MCC's is a paired series of color bars (cyan, magenta and yellow combination only) and adjacent gray (black ink only) bars distributed across an entire page. The colored bar in these figures is formed by holding cyan constant and then varying the magenta and yellow. In the figures, the color bar is on the left in each pair, and the gray bar is on the right. The user then selects the pair of bars that most closely matches each other. This choice, in turn, is used to adjust the amount of color ink on the page.
The inherent problem associated with the foregoing selection process is that the accuracy of the process is limited by human visual constraints.